In a typical radio communications network, terminals, also known as mobile stations, wireless devices and/or user equipments (UEs), communicate via a Radio Access Network (RAN) to one or more core networks. The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographical area where radio coverage is provided by the radio base station at a base station site or an antenna site in case the antenna and the radio base station are not collocated. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying the cell uniquely in the whole mobile network is also broadcasted in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the base stations.
In some versions of the RAN, several base stations are typically connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The RNCs are typically connected to one or more core networks.
A Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity.
Specifications for the Evolved Packet System (EPS) have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein the radio base station nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of a RNC are distributed between the radio base stations nodes, e.g., eNodeBs in LTE, and the core network. As such, the radio access network (RAN) of an EPS system has an essentially “flat” architecture comprising radio base station nodes without reporting to RNCs.
As stated above, the Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) comprises base stations called enhanced NodeBs (eNBs or eNodeBs), providing the E-UTRA user plane and control plane protocol terminations towards the User Equipment (UE). The eNBs are interconnected with each other by means of the X2 interface. The eNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the Mobility Management Entity (MME) by means of the S1-MME interface and to the Serving Gateway (S-GW) by means of the S1-U interface. The S1 interface supports many-to-many relation between MMES/S-GWs and eNBs. The E-UTRAN architecture is illustrated in FIG. 1.
The eNB hosts functionalities such as Radio Resource Management (RRM), radio bearer control, admission control, header compression of user plane data towards serving gateway, routing of user plane data towards the serving gateway. The MME is the control node that processes the signaling between the UE and the CN. The main functions of the MME are related to connection management and bearer management, which are handled via Non Access Stratum (NAS) protocols. The S-GW is the anchor point for UE mobility, and also includes other functionalities such as temporary DL data buffering while the UE is being paged, packet routing and forwarding the right eNB, gathering of information for charging and lawful interception. The PDN Gateway (P-GW) is the node responsible for UE IP address allocation, as well as Quality of Service (QoS) enforcement (this is explained further in later sections). FIG. 2 gives a summary of the functionalities of the different nodes, and the reader is referred to 3GPP TS 36.300 V11.4.0 (2012-12) and the references therein for the details of the functionalities of the different nodes. In FIG. 2, the logical nodes comprise functional entities of the control plane and the radio protocol layers are marked with a frame.
Traffic Offloading Using Wi-Fi
Using Wi-Fi/WLAN, the two terms are used interchangeably throughout this disclosure, to offload traffic from the mobile networks is becoming more and more interesting from both the operator's and end users point of view. Some of the reasons for this tendency are:                Additional frequency: by using Wi-Fi, operators can get an additional 85 MHz in the 2.4 GHz band and another, close to, 500 MHz in the 5 GHz band.        Cost: From operator's point of view, Wi-Fi uses unlicensed frequency that is free of charge. On top of that, the cost of Wi-Fi Access Points (AP), both from Capital Expenditures (CAPEX) and Operating Expenditures (OPEX) deployment aspects, is considerably lower than that of a 3GPP base station, BS/eNB. Operators can also take advantage of already deployed APs that are already deployed in hotspots such as train stations, airports, stadiums, shopping malls, etc. Most end users are also currently used to having Wi-Fi for free at home, as home broadband subscriptions are usually flat rate, and public places.        Terminal support: Almost all User Equipments (UEs) such smartphones and other portable devices currently available in the market support Wi-Fi. In the Wi-Fi world, the term Station (STA) is used instead of UE, and as such the terms UE, STA and terminal are used interchangeably in this disclosure.        High data rate: Under low interference conditions and assuming the user equipment is close to the Wi-Fi AP, Wi-Fi can provide peak data rates that outshine that of current mobile networks, for example, theoretically up to 600 Mbps for IEEE 802.11n deployments with Multiple Input Multiple Output (MIMO).        
A very simplified Wi-Fi architecture is illustrated in FIG. 3 and FIG. 4. On the user plane (FIG. 3), a very lean architecture is employed where the UE/STA is connected to the Wi-Fi Access Point (AP), which can directly be connected to the Internet. In the control plane (FIG. 4), an Access point Controller (AC) handles the management of the AP. One AC usually handles the management of several APs.
Security/authentication of users is handled via an Authentication, Authorization and Accounting (AAA) entity. Remote Administration Dial In User Service (RADIUS) is the most widely used network protocol for providing a centralized AAA management (RFC 2865).Access Network Discovery and Selection Function
The Access Network Discovery and Selection Function (ANDFS) is an entity defined by 3GPP for providing access discovery information as well as mobility and routing settings to the UE. ANDFS is a new entity added to the 3GPP architecture in Release 8 of 3GPP TS 23.402. A simplified ANDSF architecture is depicted in FIG. 5. As shown in the FIG. 5, the ANDSF server is only connected to the UE and its main goal is to provide the UE with access network information in a resource efficient and secure manner. The communication between the UE and the ANDSF server is defined as an IP-based S14-interface.
By supplying information about available both 3GPP and non-3GPP access networks to the UE, the ANDSF enables an energy-efficient mechanism of network discovery, where the UE can avoid continuous and energy-consuming background scanning. Furthermore, the ANDSF provides the mobile operators with a tool for the implementation of flexible and efficient UE steering of access mechanisms, where policy control can guide UEs to select one particular RAN over another. Note that this may be an overstatement if ANDSF is implemented as an “app”, since it relies on OS support and priority of ANDSF in relation to other “apps”. This condition may be only partly fulfilled, which makes the control somewhat unreliable.
The ANDSF supplies three types of information—discovery information, inter-system mobility settings (ISMP) and inter-system routing settings (ISRP). All these are summarized and implemented via ANDSF managed objects (MO), which are communicated to the UEs via an over-the-top (OTT) signaling channel, as Simple Object Access Protocol (SOAP)-XML messages.
The discovery information provides the UE with information regarding the availability of different Radio Access Technologies (RAT) in the UE's vicinity. This helps the UE to discover available (3GPP and) non-3GPP (Wi-Fi) access networks without the burden of continuous background scanning. Inter-System Mobility Settings (ISMP) are settings which guide the UE to select the most preferable 3GPP or non-3GPP access. The ISMP are used for UEs that access a single access (3GPP or Wi-Fi) at a time. The ISMP information specifies the behavior of UEs, which can be connected to only one access network at a given time (either 3GPP, WLAN, WiMAX, etc). If the UE, however, supports connection to several access networks at the same time, the operator can use the third type of information, ISRP, to increase the granularity of the RAN selection. In that case, the UEs will be provided with settings, which specify how the traffic flows should be distributed over the different RAN, for example, voice is only allowed to be carried over 3GPP RA, while Internet video streaming and best-effort traffic can be routed via WLAN. The ANDSF provides mobile operators with a tool to determine how the UEs connect to different RANs and hence allows them to add more flexibility in their traffic planning. Simplified examples of ANDSF rules are given in Table 1 and Table 2.
TABLE 1ANDSF MO - Discovery InformationAccessNetworkTypeAccessNetworkAreaAccessNetworkInfoRef3 (WLAN)Geo Location:ID = 812AnchorLatitude =AddrType = SSID5536988Addr = OperatorSSID812AnchorLongtitude =IP = <skipped>836620AuthInfo:Radius = 40AuthType = HTTP-DIGESTAuthName = UsernameAuthSecret = SecretBearerType = WLANBearerParam:SecMode = 802.1X3 (WLAN)3GPP Location:ID = 1056UTRAN_CI = 3048AddrType = SSIDUTRAN_CI = 4053Addr = OperatorSSID1056IP = <skipped>AuthInfo:AuthType = HTTP-DIGESTAuthName = UsernameAuthSecret = SecretBearerType = WLANBearerParam:SecMode = 802.1X
Table 1 consists of two access network discovery entries. The first rule, for example, states that there is a WLAN access network (with SSID “OperatorSSID812”) available in the area, described by the geographical coordinates. The second rule states that there is a WLAN access network available in two 3GPP cells, indicated by their respective cell IDs (CI).
TABLE 2ANDSF MO - ISRPRuleUpdate-PriorityForFlowBasedRoamingPLMNPolicy1IPFlow:0 (UE not240090 (UE notStartSourcePortNumber =roaming)required to22update theEndSourcePortNumber =policy)23 (SSH, Telnet)StartDestPortNumber = 22EndDestPortNumber = 23ValidityArea:AnchorLatitude = 5536988AnchorLongtitude =836620Radius = 40RoutingRules:AccessTechnology = 1(3GPP)2IPFlow:0 (UE not240090 (UE notProtocolType = 6 (TCP)roaming)required toValidityArea:update theAnchorLatitude = 5536988policy)AnchorLongtitude =836620Radius = 40TimeOfDay:TimeStart = 170000TimeStop = 180000RoutingRules:AccessTechnology = 3(WLAN)AccessId =OperatorSSID812
Table 2 contains description of two rules that apply to the same location (in this case represented by geographical coordinates). Note that the rules overlap, since the first one characterizes all data-flows carried via ports 20 to 23 (all of which usually carry TCP traffic). At the same time, the second rule applies to all Transmission Control Protocol (TCP) traffic, hence is more generic. In order to make sure that the Telnet and SSH traffic (ports 22 and 23 respectively) is carried over 3GPP RA, the first rule is given a higher priority, the lower number means higher priority.
Hotspot 2.0
Different standards organizations have started to recognize the needs for an enhanced user experience for Wi-Fi access, this process being driven by 3GPP operators. An example of this is the Wi-Fi Alliance with the Hot-Spot 2.0 (HS2.0) initiative, now officially called PassPoint (“Hotspot 2.0 (Release 1) Technical Specification”, Wi-Fi Alliance® Technical Committee Hotspot 2.0 Technical Task Group, V 1.0.0). HS2.0 is primarily geared toward Wi-Fi networks. HS2.0 builds on IEEE 802.11u, and adds requirements on authentication mechanisms and auto-provisioning support.
The momentum of Hot-Spot 2.0 is due to its roaming support, its mandatory security requirements and for the level of control it provides over the terminal for network discovery and selection. Even if the current release of HS2.0 is not geared toward 3GPP interworking, 3GPP operators are trying to introduce additional traffic steering capabilities, leveraging HS2.0 802.11u mechanisms. Because of the high interest of 3GPP operators, there will be a second release of HS2.0 focusing on 3GPP interworking requirements.
HS2.0 contains the following procedures:                1. Discovery: where the terminal discovers the Wi-Fi network, and probes them for HS2.0 support, using 802.11u and HS 2.0 extensions.        2. Registration is performed by the terminal toward the Wi-Fi Hot-spot network if there is no valid subscription for that network.        3. Provisioning: Policy related to the created account is pushed toward the terminal. This only takes place when a registration takes place.        4. Access: cover the requirements and procedures to associate with a HS2.0 Wi-Fi network.        
One of the attractive aspects of HS2.0 is it provides information for the STA that it can used to evaluate the load of the Wi-Fi network before attempting the authentication process, thereby avoid unnecessary connection to highly loaded Wi-Fi network. The load conditions that the STA can evaluate are the following:                BSS load element—This is actually a part of the original IEEE 802.11 standard and provides information about the AP population and the current over-the-air traffic levels, as shown in FIG. 6. It is obtained either via a Beacon or a Query Response frame and is used for vendor-specific AP-selection algorithms. The element is described in detail in Chapter 8.4.2.30 of IEEE 802.11. The most relevant field is the “Channel Utilization” field, which states the amount of time that the AP senses the medium as busy.        WAN metrics element—is one of the extra features that HotSpot™ 2.0 adds to the IEEE 802.11u amendment. The element, illustrated in FIG. 7, can be obtained via an Access Network Query Protocol (ANQP) query (by requesting the element “ANQP Vendor Specific list”) and it provides information about the AP's uplink/downlink WAN (backhaul) speed, as well as the uplink/downlink load. The element is described in detail in Chapter 4.4 of the HS2.0 specification.Current Behavior of Terminals Supporting 3GPP and Wi-Fi        
Most current Wi-Fi deployments are totally separate from mobile networks, and are to be seen as non-integrated. From the terminal's perspective, most mobile operating systems (OS) for UEs such as Android and IOS, support a simple Wi-Fi offloading mechanism where the UEs immediately switch all their Packet Switched (PS) bearers to a Wi-Fi network upon a detection of such a network with a certain signal level. The decision to offload to a Wi-Fi or not is referred henceforth as access selection strategy and the aforementioned strategy of selecting Wi-Fi whenever such a network is detected is known as “Wi-H-if-coverage”.
There are Several Drawbacks of the Wi-Fi-if-Coverage Strategy (Illustrated in FIG. 8):
                Though the user/UE can save previous passcodes for already accessed Wi-Fi APs, hotspot login for previously unaccessed APs usually requires user intervention, either by entering the passcode in Wi-Fi connection manager or using a web interface.        Interruptions of ongoing services can occur due to the change of IP address when the UE switches to the Wi-Fi network. For example, a user who started a VoIP call while connected to a mobile network is likely to experience call drop when arriving home and the UE switching to the Wi-Fi network automatically. Though some applications are smart enough to handle this and survive the IP address change (e.g. Spotify), the majority of current applications don't. It also places a lot of burden on application developers if they have to ensure service continuity.        No consideration of expected radio performance is made, and this can lead to a UE being handed over from a high data rate mobile network link to a low data rate via the Wi-Fi link. Even though the UE's OS or some high level software is smart enough to make the offload decisions only when the signal level on the Wi-Fi is considerably better than the mobile network link, there can still be limitations on the backhaul that the Wi-Fi AP is using that may end up being the bottle neck.        No consideration of the load conditions in the mobile network and Wi-Fi are made. As such, the UE might still be offloaded to a Wi-Fi AP that is serving several UEs while the mobile network (e.g. LTE) that it was previously connected to is rather unloaded.        No consideration of the UE's mobility is made. Due to this, a fast moving UE can end up being offloaded to a Wi-Fi AP for a short duration, just to be handed over back to the mobile network. This is specially a problem in scenarios like cafes with open Wi-Fi, where a user walking by or even driving by the cafe might be affected by this. Such ping pong between the Wi-Fi and mobile network can cause service interruptions as well as generate considerable unnecessary signaling, e.g. towards authentication servers.        
In order to combat these problems, several Wi-Fi/3GPP integration mechanisms have been proposed.
RAN Level Integration
A good level of integration of 3GPP and Wi-Fi can be realized via access selection based on RAN information on both 3GPP and Wi-Fi, in addition to the common authentication and user plane integration methods discussed above. This is illustrated in FIG. 9.
A functional entity known as a Smart RAN Controller (SRC) can be introduced that is used as an information sharing point for the Wi-Fi and 3GPP networks. Optimal traffic steering can then be performing by considering the situation at each network. Using such an abstraction, even legacy UEs could be able to benefit from Wi-Fi integration. For example, consider a legacy UE that is already connected to a 3GPP network, and employing “Wi-Fi if coverage” access selection mechanism comes to a Wi-Fi coverage area. When the UE tries to connect to the Wi-Fi network, the Wi-Fi AP/AC can connect to the SRC to request information about the current user's Quality of Service (QoS) in the 3GPP network, and if it is found that the user's QoS is going to be degraded if the connection is switched to Wi-Fi, a rejection could be sent to the UE from the Wi-Fi in order keep it connected to the 3GPP network. A tighter integration can also be formed if the Wi-Fi AP and eNB are co-located and have direct communication between them rather communicating via the SRC (similarly one can think of direct communication between the AC, RNC, BSS, etc. . . . ).
Policy Based WI-FI-3GPP Integration
ANDSF settings are either static or semi-static, and they're not adaptive to fast changing radio environments and system loads. Even though it is possible to enhance the ANDSF to include radio link quality into the settings, the current mechanism limits update frequency of the polices. Therefore it is not capable of guiding the terminal to an access which provides better quality of experience (QoE).
In terms of 3GPP interworking, HS2.0 is mainly to improve usability and facilitate access selection by providing the Wi-Fi loads. It is not expected that HS2.0 will support operator controlled dynamic access selection.
The ANDSF and HotSpot2.0 mechanisms described above are not targeting tight integration of Wi-Fi considering network information, e.g. load in different accesses, bitrates, etc. The reason for this is that the exact UE behaviour is not specified and the parameters do not include radio information. There is however work starting in 3GPP SA2 and Wi-Fi Alliance HotSpot2.0 Release 2 to enhance ANDSF to take into account the Hotspot 2.0 solutions. One example is that the ANDSF policy could define UE actions based on the information received from the Wi-Fi AP about the BSS load and WAN metric. FIG. 10 shows an example of the Integration of ANDSF and HS 2.0.
UE based solutions such as the currently available ones in Android and IOS based phones have several drawbacks as described above. Network based solutions such as ANDSF, as mentioned above, use rather static rules and they don't reflect current network conditions. RAN level integration via SRC is able to consider both UE and network performance in a dynamic fashion. However, the SRC based solution can become complex to realize as there is a need to maintain the context of each UE in the different access network. Also, each offloading decision requires the involvement of the SRC entity and a UE in IDLE mode in 3GPP and not connected to Wi-Fi will not be able to utilize the benefits of SRC based solutions.
A mechanisms for Wi-Fi-3GPP integration has been suggested that enables dynamic operator control over access selection and traffic steering between access networks by defining a number of semi-dynamic policy sets for each terminal. The dynamic network policy index can be broadcasted to all terminals or/and communicated in a unicast fashion to a given terminal to indicate a proper settings to use. A terminal selects one policy based on its current state, such as connection status and ongoing traffic.
Wi-Fi/3GPP Deployment Scenarios
The different deployment scenarios for Wi-Fi can be categorized into three groups as Private Wi-Fi, Public Wi-Fi and Integrated Wi-Fi. This is illustrated in FIG. 11 and the different scenarios are explained below:
Private Wi-Fi (Residential, Enterprise)                Access selection controlled by end user        Operator services supported over the top and/or with S2b (S2c)        No charging        
Public Wi-Fi (3rd Party, Operator/Shared Hotspot)                Access selection depending on roaming agreements, end user, etc.        Possible to use HS2.0 mechanism for authentication, e.g. Extensible Authentication Protocol-Subscribed Identity Module (EAP-SIM), and roaming                    Access selection based on operator settings (ANDSF/HS2.0) may be supported in the future terminals.                        Operator services supported over the top and/or with S2b (S2c)        Different charging models typically used in Wi-Fi compared to cellular (e.g. flat-rate, bucket charging).        
Integrated Wi-Fi (Wi-Fi as a Part of Heterogeneous Network)                Wi-Fi network is managed by the operator.        Access selection controlled by operator via network based mechanism and/or ANDSF/HS2.0 settings sent to the UE        Seamless Wi-Fi offloading experience for end user (i.e. user does not need to care about which interfaces are used for the traffic)        All operator services supported using smart service selection and user plane integration (e.g. S2a, S2b over trusted Wi-Fi)        Possibility to optimize network performance and end user experience        Future support for seamless IP session continuity        Similar charging model in Wi-Fi and cellular.        
For the Private and the Public Wi-Fi (Wi-Fi roaming) scenarios it is expected that only limited network control can be used due to e.g. different charging models typically used in Wi-Fi compared to cellular. Examples of network control mechanisms that could be also applicable in these scenarios are ANDSF and HS2.0. The performance of the radio communications network may be reduced when the terminal uses same settings related to accessing the radio communications network moving between cells in the radio communications network.